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Using a Rotary Position Sensor

Posted: Fri Nov 16, 2012 8:58 am
by kd5crs
I found these while poking around Digikey:

http://www.digikey.com/product-detail/e ... ND/2080232

It is called a rotary position sensor, and the data sheet (http://www.bourns.com/data/global/pdfs/3382.pdf) says it is used for things like dishwasher controls and audio controls.

Can you put it on a shaft and have a really cheap ($2.52) absolute rotation measurement device? It looks like it is identical to a rotary potentiometer. Most rotary pots are only rated for 10K cycles, but this thing says it is good for 1M.

Has anyone ever used these, and is there a catch? Because it seems to me like it is much better than a much more expensive rotary pot or a rotary encoder.

Thanks.

Re: Using a Rotary Position Sensor

Posted: Fri Nov 16, 2012 9:08 am
by waltr
Never used one but the data sheet indicates that it has continuous rotation so could be used for the position of a rotating shaft.
One gotch may be what happens when the wiper reaches the end of the resistive element and jumps to the other end. Does the resistance at the wiper go open or glitchlessly change from maximum to minimum resistance.
Nice part if it is glitchless and cheap.

Re: Using a Rotary Position Sensor

Posted: Tue Nov 20, 2012 5:39 pm
by Duane Degn
waltr wrote:One gotch may be what happens when the wiper reaches the end of the resistive element and jumps to the other end. Does the resistance at the wiper go open or glitchlessly change from maximum to minimum resistance.
The datasheet says "Adjustment Angle 330 degress nom.", it looks like there's 30 degrees with infinite resistance.

Still a pretty cool sensor.

Re: Using a Rotary Position Sensor

Posted: Tue Nov 27, 2012 3:10 pm
by kd5crs
I received them and tried them out. You are both correct, it freely rotates 360 degrees but 30 degrees are infinite resistance. So I guess if you need perfect 360 degree positioning you would just use two.

I got one of the 4mm shaft gear motors Pololu sells, and ground the flat an additional 0.5mm. The sensor fits that D perfectly, and you can solder the top pin on the sensor to the motor to hold the sensor stator in a fixed position. Preliminary tests show that the sensor is very repeatable. I'll let you know if it makes it to the claimed 1M cycles.

Re: Using a Rotary Position Sensor

Posted: Tue Nov 27, 2012 5:26 pm
by waltr
Ok. Thanks for the info on this sensor.
Neat idea on using two sensors to fill in the 'dead zone'.

Re: Using a Rotary Position Sensor

Posted: Tue Nov 27, 2012 7:32 pm
by Mee_n_Mac
Wouldn't using 2, offset and in parallel, lead to a non-monotonic R-vs-angle curve ? You'd end up with some positions that have the same resistance as other positions. Using 2 into 2 A/D channels and some "smarts" should work though.